Wire antennas for listeners
How to select your antenna ? (III)
Practically you will soon discover that to get good results, you will have to take into account technical considerations as e.g. the use or not of coils or traps on the antenna, the numbers of radials attached to a vertical, the numbers of elements on a beam, what type of coax is used, etc.
In the field while checking the free space available you will maybe discover that it is impossible to set up the antenna very high due to the presence of trees or power lines, the lack of infrastructure (supporting wall, long pole, tree, etc), due to wind blowing in average too strong or a servicing impossible to ensure due to obstacles.
Once your specifications defined comes the choice of the antenna. Each model has its advantages. Take a few examples:
- A Marconi vertical displays a low profile, is relatively light and its radiation pattern is omnidirectional
- A vertical should come with its own ground plane (radials or counterpoise) to generate its mirror image
- A monoband antenna displays optimum performances with a SWR close to 1:1
- A wire antenna (dipole, beam, quad) is light, very easy to install and perfect for listening purposes
- An antenna placed on top of a pylon 20 m high will get the best radiation pattern for bands between 40-10m
- A free-standing pylon or a tower using a lift will probably never collapse if you secure it with guy wires
- A directive antenna (Yagi, log, quad, etc) is the best "gun" for DXing
But advanced amateurs will concede that the same antennas have also drawbacks :
- A Marconi vertical captures much QRM due to its vertical polarization similar to the one of man-made emitters
- A high-end vertical with all its radials can be bulky and be a danger for kids or even adults wandering near
- A monoband antenna is by definition too restrictive if you want to listen to several bands
- Placed below 1/2l over ground, the radiation pattern of an antenna is altered by ground effects (in emission)
- A tower need sometimes a permission to be erected and is not really a stealth installation
- Handling with ease an antenna placed on top of a 10 m high pylon can be expensive when security is an issue
- Any pole erected permanently and higher than about 5m needs guy wires to prevent any accident
- A directive antenna (Yagi, log, quad) is cumbersome and requests a free area of about 10x10x10m, a robust mast and a rotator.
If all these features are of your concern there is maybe no solution satisfying your needs. Maybe. But if you are not too hard to please, that you are a licensed ham or a listener, and if you can be satifyied with cheap solutions, there are several, among which short verticals and wire antennas. Among these last name the long wire, the dipole, the beverage, the wire beam, the loop, etc. These are as much designs that are usually much cheaper than a true multielement directive array like a beam or a quad.
To read : Your first antenna – the half-wave dipole, SRGB
Where and how to place a receive wire antenna ?
Contrary to the emission, to receive stations in a first time you do not need a special antenna, even not a compact magnetic loop or a vertical which, if they are more selective, are much more expensive, and the vertical requests some space outdoor or at least a balconery and good fixings to give good results and prevent any accident. As not everybody can install a beverage antenna or a beam, to avoid you making useless tests trying to find the best size and configuration, here are some ideas to apply according your choice.
When space is very limited, when you live in a studio or an appartment and you have neither access outdoor nor on a balconery, you are unvolontarily restricted to install your antenna indoor. In this case the best to do is to buy some dozen meters of solid copper wire or a thin steel wire and to fix it around the room of your shack at ceiling level. Make the wire run some turn around the room and don't worry to keep it straight as that will not influence the receiving. Attach one end where you can around a nail or a screw-eye and connect the other end to your receiver antenna plug, without worry to place the system to the ground; you are inside, isolated under cover of your roof and lightning conductors.
This solution can give satisfactory results. It is far to be optimized and you will be probably disturbed by a lot of interferences, including your own if you use a switched power supply or very old gears badly protected. These interferences can also come from the coupling of your antenna to your house wiring system if wires exceed 1/4l, with the gutter or the plumbing.
Note that this solution is not at all suited for emission as it probably lost all its energy in the transmission line radiation (SWR infinite). But you will always be able to listen the loudest stations coming from the other side of the Earth if they bear their antenna to your direction. Of course if you live in Europe all european stations will arrive loud and clear, including some DX from UA9, JA, W6, KL, PY, some from Africa (CN, 7X, 5Z) and the Middle East (4X, 9K, etc), you will hear easily most contesters (e.g. during Field Days or CQ WW activities) and some DX-peditions too. For these last, that will depend on number of factors that we explained in other pages dealing with propagation and how to hear DX stations as SWL.
Another solution, but more expensive, is to buy an small active antenna that you can place a few meters from your receiver or in your attic. However this device amplifies both the signal and electric noises, mainly human made as it will be installed indoor. This vertical antenna is also very short (0.5-2m long). In such a configuration it captures easily harmonics and RFI generated by various devices usually not protected (old TV, VCR, TL, dimmer, boiler, pager, microwave oven, unshielded plug, etc). So as soon as possible try to install your antenna outdoor to reduce noise.
A better solution is to install an active magnetic loop like Wellbrook 1530 in horizontal or vertical position. This aerial in form of a loop of 1m in diameter (its diameter is about 1/10l) gives much better results than any indoor long wire or whip antenna but it is more expensive too. If you have some money left, you can also install a large mobile vertical antenna like the very appreciated Hi-Q models or one of its competitors. Their overall height does not exceed 3m and their weight is less than 5 kg.
If you install your antenna indoor using any length of wire, untuned, an external antenna tuner or matching box will be probably more than necessary to obtain the state of resonance on each band (see page 4). Remember that the SWR does not intervene in receiving as you do not emit but an untuned antenna will not pick up correctly signals that will be thus weaker than using a fine-tuned system.
At last know that some stupid things can be tested with more or less success indoors or outdoors. Differences are huge and... audible. For example, avoid to keep extra lengths of coaxial, they require space and capture QRM; avoid to enrol the 100 m of your antenna on your desktop (but as using a dummy load, you will hear signals from near stations !); avoid to place your antenna on the soil or in a closed room (in your shack) at the risk to reduce substantially the overall signal of wavelengths from 20 meters and longer (the signal strength can drop from RS-57 to 45 and below for a remote station). So forget these amateur solutions and try to respect the rules if you want to get good results.
Outdoor installation : through the window or on the balconery
Due to the suppression of the house armed concrete structure as well as all domestic sources of QRM, any small antenna located a few meters outdoor will give better results than any indoor installation.
The balconery for example will be used to take advantage of the free space to get a better receive and to reduce artificial noises generated indoor by electronic home devices.
If you live in an appartmlent or a building, if there is no conflict with the neighborhood, you can hang a long wire through the window along the external wall or from the balconery up to 10 or 20 m below, stopping the wire over 4 m from the ground for the safety of pedestrians and prevent that someone robes it. To tight it like a plumbline and prevent it to coil up, attach a fishing weight or a small steel plate at the end. Do not attach it to the wall in order to be able to wind it up easily. However these solutions are really not optimized.
A balconery or a vasistas can also be favorably used to install a magnetic HF loop or a large mobile antenna. As we told, this antenna gives excellent results in reducing noises and increasing the selectivity of amateur radio stations.
But if you use a long wire, remember well that the wire segment running indoor to the receiver is very sensitive to man-made interferences and should be isolated using a coaxial segment on all its length. Of course this part will probably not pickup the least radio wave, except the stronger emitters.
If this solution is not always efficient in removing RFI, it can, in some cases, reduce its intensity of some tens of dB. Avoid also to cross several rooms with your coax or you will be unable to close your doors and have probably to find a way to hide the cable running in the middle of your hall or in the living room ! For this reason and technical considerations (RFI pickup) limit your indoor segment to the strict minimum (1 meter or so) and try to install your receiver close to a window of an opening to the outside through which you could throw your coaxial.
To read: RFI, troubles and solutions
Permanent outdoor installation
One of the cheapest antenna tuned for HF bands is unquestionably the multi-band dipole (G5RV, W3DZZ, etc) or the Carolina Windom that costs between 50-110$/€ if you don't want to build it yourself. Measuring between 20 and 100 m long (HF reception is optimized with any length multiple of 18-20m), tight as high as you can above the ground, such an antenna is very discrete, cheap, quickly removable and can be installed in many places, more of less open to the sky.
Better, light and easy to collapse, you can use your dipole on portable operations or during a contest, and even take it with you on holidays. Like a long wire and other Windom, there is really no disavantage of using such low cost antennas, excepting that they require some free space in length and in height. The alternative is to erect a short vertical (3-6m high) or a mobile antenna. But like all vertical, they request either an excellent ground plane (usually the mobil'home or the car hard top) or additional flexible radials that will run on the ground over 5m from the antenna base.
To be complete, remind that placed horizontally in their classic configuration, dipoles are of course not much directive compared to directional arrays (beam, quad). They usually show 2 symmetrical lobes in the azimuthal plane (4-clover or X-shape), and you will have difficulties to hear signals from some directions where they are no pick-up lobes or very small ones (e.g. if you wire antenna is tight in a N-S direction, there are nulls more or less deep to the N and to the S).
These antennas can however be directive, offering about 4 dBd gain, either if you tight them very high (over 10m above ground for the 20m band), or if you extend their length over 40m, or if you fold them horizontally (horizontal V-shape) or in slope (L-shape), these two last designs open at about 120°. The directivity is very appreciable but of course it is fixed.
If you need more information, read the article titled From Long wire to Yagi in which I review the various antenna designs and their performances.